Photographic emulsion having a low modulus of elasticity and process for its manufacture



United States Patent Office 3,359,108 Patented Dec. 19, 1967 ABSTRACT OF THE DISCLOSURE Photographic emulsions having a low modulus of elasticity are obtained by preparing an aqueous dispersion of silver halide in a binder composed of approximately 70-97% (dry weight) of a water insoluble hydrophobic material such as a styrene-butadiene latex and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides (e.g., gelatin). Preferred emulsions contain colloidal silica.

This invention relates to the preparation of photographic silver halide emulsions having a low modulus of elasticity characterized in that the binder thereof consists mainly of a synthetic elastomer and to the photographic products obtained using such an emulsion.

Attempts have been made to prepare emulsions having a low modulus of elasticity which would be particularly advantageous in combination with film bases likewise having a low modulus of elasticity. In certain cinematographic applications projectors are used whose light source is extremely powerful, often producing dimensional variations of the emulsion layer and change in the curvature of the film being passed throughout the projector thus requiring constant adjustment.

One object of our invention is to provide a photographic emulsion having a low modulus of elasticity, the vehicle of which contains but a small amount of gelatin or other hydrophilic binder, the binder consisting mainly of hydrophobic material. Another object of our invention is to provide a photographic emulsion which owing to its low modulus of elasticity, ofiiers excellent dimensional stability on thin supports and which does not curl particularly when used in film projectors with an intense light source. A further object of our invention is to provide silver halide photographic emulsions in which a synthetic resin latex is primarily employed as the carrier but to which has been added a hydrophilic material of the nature of colloidal silica whereby better permeability of the emulsion coatings to processing solutions is obtained. A still further object of our invention is to provide a process for the manufacture of a photographic emulsion which is very useful for both black-and-white and color photography. A still further object of our invention is to prepare photographic products of good physical characteristics. Other objects of our invention will appear herein.

Photographic emulsions in accordance with the present invention ofier various advantages such as (1) they can withstand elevated temperatures thus permitting developing at such elevated temperatures which may make for rapid development, (2) they will self-harden following drying without the addition of hardeners owing to coalescence of the particles of the hydrophobic binder.

Photographic emulsions in accordance with the invention are characterized by the fact that they contain as a binder from 70 to 97% (based on total binder) of a hydrophobic material that is water insoluble and which is incorporated in the form of a latex and from 330% of total binder of a hydrophilic binder as for example gelatin.

For preparing the emulsion according to the invention a coagulum of silver halide is mixed with a latex of a hydrophobic binder generally made up of a polymer particularly a synthetic elastomer followed by ripening and the adding thereto of the customary adjuvants such as sensitizers and the like. The emulsion composition is coated on a film base to achieve, following drying, an emulsion layer offering a low modulus of elasticity. The

spherical particles of the polymers coalesce together while confining the silver halide grains. Under these conditions the resultant emulsion layer has a relatively low permeability to aqueous media and to photographic baths at normal processing temperatures. The permeability increases with the ratio of silver halide to binder and with an increase in the ratio of hydrophilic to hydrophobic binder. It was found that advantageous results can be achieved with the latter ratio between 30:70 and 15:85. In the case of lower ratio it is necessary to develop at a relatively elevated temperature that is to say at about C. or higher. Permeability to photographic baths is increased by introducing such a hydrophilic compound as colloidal silica, a polyoxyethylene glycol, dialkyl silicate, polyvinyl pyrrolidone or starch into the layer. Incorporated into the emulsion may be any value from 5100% and preferably 10-80% of the said hydrophilic compound based on the weight of the binder solids already in the emulsion.

Among the polymers usable in accordance with our invention as a hydrophobic binder used in the form of its latex can be mentioned styrene-butadiene copolymer, polychloroprene, polyvinyl acetate resulting from copolymerizing vinyl acetate with other monomers to provide plasticization, butyl rubber (isoprene-isobutylene copolymer), polyisoprene, polybutadiene-cis and the like.

As for the hydrophilic constituent gelatin is preferably used. However, some other hydrophilic binder such as for example polyvinyl pyrrolidone may be employed in this connection. For instance, a good dispersion of silver halide grains may be obtained by dispersing silver halide coagulum at 40 C. in the presence of polyvinyl pyrrolidone then adding the latex of the hydrophobic binder 'only after the silver halide grains have been well dispersed. The polyvinyl pyrrolidone often increased the maximum optical density and the rate of development. The polyvinyl pyrrolidone is preferably used in an amount of approximately 10% based on the hydrophobic binder solids.

In the present specification the term coagulum designates a dispersion of silver halide in a very slight amount of a gelatin compound such as prepared in a grain wash process for example that described in Yutzy and Frame US. Patent No. 2,614,928. According to this process an aqueous solution of a silver salt e.g. a silver nitrate is mixed with a water soluable halide such as potassium bromide in an aqueous solution of a gelatin derivative capable of being coagulated by an acid as for example a derivative of gelatin and a dicarboxylic acid anhydride as described and claimed in Yutzy and Frame U.S. Patent No. 2,525,753. After the silver halide dispersion is prepared it is coagulated by lowering the pH and the coagulum thus formed is separated from the liquids. This coagulum can be dispersed in a binder such as gelatin or in accordance with the invention it can be dispersed in a hydrophobic binder.

Furthermore, in accordance with the invention the coating of photographic emulsions prepared thereby may be facilitated in certain cases by adding materials which act as thickeners as for example a latex of a copolymer having an acrylic base, sodium polyacrylate, bentonite or the like. These compounds may be considered hydrophilic and therefore their presence also improves the penetration of the emulsion layer by processing baths.

The emulsions according to the invention are stable and can be stored for several months at ordinary temperature without the appearance of fog. As the polymer of the latex added to the emulsions according to the invention is an organic polymer capable of swelling in certain nonaqueous solvents, it is possible to achieve an image by soaking the exposed film in an organic solution of a reducing agent in a basic medium. Solvents suitable for this purpose are for example acetone, dimethyl formamide, ethylene glycol and the like.

The adhesion of emulsion layers in accordance with the invention is good on various supports such as subbed cellulose triacetate or polyethylene terephthalate film base, paper (preferably baryta coated), glass, etc.

The emulsions according to the invention can be used for either black-and-white or color photography. In the lattercase they may be used in color reversal processes in which the color former is incorporated in the baths or in negative-positive processes in which the color former is incorporated in the emulsion layers.

These emulsions for the reasons indicated above are especially suitable in the preparation of motion picture film.

The following non-limiting examples are illustrative:

Example 1 A silver halide coagulum was prepared from a silver nitrate solution and a solution of alkali metal bromide and iodide, which solutions were added simultaneously to an aqueous solution of a gelatin derivative as the peptizing agent as described in Example of U.S. Patent No. 2,614,928. 40 grams of this coagulum which contains 3 grams of gelatin was made to swell in 155 ml. of water at 40 C. One hour later ml. of an equeous 25% polyvinyl pyrrolidone solution was added and the mixture was maintained at 45 C. for another hour.

Just prior to coating 45 ml. of a styrene-butadiene latex containing 49.5 grams of solids per 1 00 ml. was added. Also added was 2 ml. of saponin and normal solution of acetic acid was added to adjust the pH to 6. The mixture was coated onto a baryta coated paper (135 grams) and dried in the drier at 50 C. The binder of the emulsion layer applied to the paper was made up of 80% of hydrophobic and 20% of hydrophilic hinder, the latter being approximately 10% gelatin and 10% of polyvinyl pyrrolidone. The resulting photographic paper was exposed under a negative and was developed for 1 minute at 25 C. in a hydroquinone type developer. The paper was then washed for 3 seconds and was treated in a conventional thiosulfate fixing bath for 10 minutes. Several exposures had been made varying the time of exposure from 0.5 to 10 seconds with appropriate aperture changes and in all instances well-contrasted images with good sharpness were obtained.

Example 2 40 grams of coagulum of that produced as described in Example 1 and containing 3 grams of gelatin was made to swell in 140 ml. of water at 45 C. There was then added 5 ml. of an aqueous 25% polyvinyl pyrrolidone solution and the mixture was maintained at 45 C. for one hour. The product thus obtained was coated out onto a paper support after adding, just prior to coating, 124 ml. of styrene-butadiene latex containing 49.5 grams of dry matter per 100 ml. and 2 ml. of saponin and the pH was adjusted to 6 by means of a normal solution of acetic acid. The emulsion was coated on 135 gram baryta paper and dried at 50 C. The binder was composed of 92% of hydrophobic and 8% of hydrophilic binding material. The paper thus obtained was exposed under a negative and processed as described in Example 1. A well contrasted image was thereby obtained.

Example 3 grams of silver halide coagulum the preparation of which is described in Example 1 which coagulum contained 12 grams of gelatin was made to swell in 620 ml. of water at 45 C. and the pH was adjusted to 6. One hour later there was added thereto 200 ml. of styrene-butadiene latex containing 99 grams of dry matter brought to a pH of 6. Also added was 8 ml. of saponin and the pH of the entire mass was again adjusted to 6. The emulsion was subjected to digestion in the presence of the customary sensitizers which had been added previously to the addition of the styrene-butadiene latex. The emulsion was coated onto paper and dried as described in the preceding examples. It was then exposed under a negative and developed for 4 minutes at 25 C. by a developer made up as follows:

Lukewarm water (approximately 50 C.) ml

Elon (methyl p-aminophenol sulfate) g Anhydrous sodium sulfite g 38 Hydroquinone g 6 Anhydrous sodium carbonate g 19 Potassium bromide g 0.9 Citric acid g 0.7 Potassium metabisulfite g 1.5

Cold water sufficient to make 1 liter.

The paper was then fixed in a conventional hypo fixing bath. This emulsion was found to compare favorably with an ordinary fine grain silver bromoiodide emulsion.

Example 4 Example 5 A photographic emulsion was prepared as described in Example 1 (using 10.5 grams of the silver bromoiodide emulsion, 5 ml. of an aqueous 25% polyvinyl pyrrolidone solution, 22 ml. of styrene-butadiene latex and 50 ml. of water). Just prior to coating out of the emulsion layer a red sensitizer was added. These procedures were re peated except that to one portion 'of emulsion a green sensitizer was added and to a second portion a different red sensitizer was supplied. Following coating on a support and drying, the three specimens were exposed behind a color sensitometric wedge having a progression of 0.1. The results obtained were similar to those achieved with gelatin binder emulsions. With the emulsions according to the invention, a gain of 3-8 steps of the sensitometric wedge was noted depending on the type 'of coloring material, the amount incorporated and the exposure time.

Examples 6 to 10 Emulsions according to the procedure described in Example 1 were prepared using for each emulsion a latex such as mentioned in the following table:

Emulsions were obtained whose layers exhibited a good modulus of elasticity and good photographic properties.

Color Developer:

Developer 1 grams 3 Anhydrous sodium sulfite do 5 Sodium carbonate do 50 Potassium thiocyanate do 0.5 Water liter 1 Color former grams 4.7 Methyl alcohol ml 100 1 N,N-diethyl-para-tol uylenediamine chlorhydrate. 2 Dihydroxy-l,5-dibromo-2,6-naphthalene.

The emulsion layer was then bleached for 5 minutes in a bleaching bath having the following composition:

Glacial acetic acid ml 5 Concentrated hydrochloric acid ml 5 Quinone grams 3.4

Water to make 1 liter.

and finally fixing was carried out for ten minutes in a standard hypo fixing bath. A cyan image was thus produced.

Example 12 An emulsion with an incorporated color former for color photography was prepared from the following.

Composition:

Silver chlorobromide coagulum grams 50 Polyvinyl pyrrolidone at 25% in water ....ml 7.1 Styrene-butadiene latex ml 32 (49.5 grams of dry matter per 100 ml.) Distilled water ml 235 Cyan color former grams 3 Tricresyl phosphate ml 6.4

The cyan color former used in this composition was 2-(2,4-di-tertamylphenoxy)-acetamino 4,6 dichloro-S- methylphenol. This composition was prepared by swelling the coagulum in distilled water at 40-45 C., adding the polyvinyl pyrrolidone solution, holding for 2 hours at 40 C. The color former was dissolved in tricresyl phosphate at 130-135 C. and the resulting hot solution was dispersed in the styrene-butadiene latex in an homogenizer. This dispersion was rapidly added to the swelled coagulum. The mixture thus obtained was coated on paper following the addition of wetting agent to the composition. The photographic paper thus obtained was exposed, developed in a color developer and treated in a stop bath followed by bleaching and fixing thereby obtaining a cyan image.

Examples 13 and 14 Example 12 was repeated except that the cyan color former was replaced by a magenta color former and a yellow color former used in the same proportions to achieve, after processing, magenta and yellow prints, respectively.

The emulsions according to the invention are especially useful for photomechanical processes particularly in typographical process where the image produced must be reversed. A standard film for this purpose comprises a photosensitive emulsion coated on a thin permanent support joined to a second temporary support of greater thickness from which it may be separated during processing.

Said film comprises ordinarily six layers: a provisional support such as subbed triacetate, a gelatin layer having a low melting point in water thus making possible the separation in a lukewarm water bath of this provisional support from the other layer, a permanent thin nitrocellulose support, a substratum for the nitrocellulose film,

an emulsion layer and finally a transparent antiabrasion coating. The emulsions in accordance with our invention make it possible to prepare a product much less complex in nature comprising a provisional support, e.g., a terephthalic polyester support, a gelatin layer having a low melting point in Water and a photosensitive emulsion layer having a low modulus of elasticity according to the invention with a transparent antiabrasion coating. The permanent support and substratum are eliminated owing to the use of an emulsion according to the invention which offers much greater mechanical resistance than previously. Furthermore, one may use a peeling or stripping layer containing a gelatin of lower grade than in previous products thus providing better resistance in the dry state and easier and faster peeling in hot water.

This example illustrates emulsions in which a hydrophilic material in addition to gelatin is used.

Example 15 A coagulum of silver bromoiodide was prepared from a silver nitrate solution and a solution of potassium bromide and iodide added to an aqueous solution of a gelatin derivative, a peptizing agent as described in US. Patent No. 2,614,928. 9.1 grams of the so prepared coagulum containing 0.7 gram of gelatin was swollen in Water and the swollen coagulum was then dispersed in a mixture of 5 ml. of styrene-butadiene latex, 5.5 ml. of an aqueous dispersion of colloidal silica the particle size of which is less than 0.03 micron (presently marketed under the names Syton and Ludox) and 30 ml. of distilled water. The dispersion was carried out in a bath thermostatically controlled at 40 C. After thoroughly mixing, the resultant emulsion was adjusted to a pH of 5.5 by means of a dilute aqueous solution of acetic acid. The binder contained 0.7 gram of gelatin per 2.5 grams of styrene-butadiene copolymer or 78% of hydrophobic binder and 22% of gelatin (based on dry weight). The emulsion thus prepared was coated upon a support to form a photosensitive product.

The following example illustrates the use of an emulsion prepared in accordance with the invention in preparing film useable in photomechanical processes.

Example 16 To a subbed polyethylene terephthalate support an aqueous solution containing 2% gelatin was applied. Following drying there was coated thereon a silver halide emulsion containing styrene-butadiene binder, the preparation of which is described in Example 1. After drying, the film thus produced was exposed, developed and fixed in the usual manner. To transfer the emulsion layer the film was placed in boiling water for 1 /2 minutes. The film was then rapidly applied by means of a roller against a subbed triacetate sheet with the emulsion surface against the substratum. The provisional polyethylene terephthalate support was then easily stripped olf. This was followed by drying of the cellulose triacetate film bearing the processed emulsion which is reversed with respect to the image of original exposure.

The invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver halide in a binder composed of approximately -97% (dry weight) of styrene-butadiene latex and at least 3% (dry weight) of hydrophilic material consisting principally of gelatin which emulsion contains 5100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 microns.

2. A photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver ha- 7 lide in a binder composed of approximately 70-97% (dry Weight) of styrene-butadiene latex and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides which emulsion contains 100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

3. A photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver halide in a binder composed of approximately 7097% (dry weight) of a water insoluble hydrophobic material and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides which emulsion contains 5-100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

4. A photographic emulsion in accordance with claim 2 wherein the hydrophilic material consists essentially of a mixture of gelatin and polyvinyl pyrrolidone.

5. A photographic product composed of polyethylene terephthalate film base bearing thereon a layer of a photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver halide in a binder composed of at least 7097% (dry weight) of a water insoluble hydrophobic material and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides which emulsion contains 5100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

6. A photographic product composed of cellulose triacetate film base bearing thereon a layer of a photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver halide in a binder composed of at least 7097% (dry weight) of a water insoluble hydrophobic material and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides which emulsion 8 contains 5-100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

7. A photographic product composed of baryta coated paper bearing thereon a layer of a photographic emulsion having a low modulus of elasticity comprising an aqueous dispersion of silver halide in a binder composed of at least 97% (dry weight) of a water insoluble hydrophobic material and at least 3% (dry weight) of a hydrophilic material, having the properties of a protective colloid for silver halides which emulsion contains 5-100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

8. A photographic product comprising a baryta coated paper base bearing thereon a photographic emulsion layer comprising silver halide in a binder composed of approximately 7097% (dry weight) of styrene-butadiene resin and at least 3% (dry weight) of hydrophilic material consisting essentially of a mixture of gelatin and polyvinyl py-rrolidone which emulsion contains 5-100%, based on the total binder, of colloidal silica the particle size of which is less than 0.03 micron.

9. A photographic product comprising a baryta coated paper base bearing thereon a photographic emulsion defined in claim 1.

References Cited UNITED STATES PATENTS 2,607,683 8/1952 Yackel et al 96-114 XR 2,836,494 5/1958 Overman 96114 XR 2,852,386 9/1958 Tong 961 14 2,976,250 3/1961 Walford 96-94 XR 3,220,840 11/1965 Yackel et al 96-1 14 XR 3,252,801 5/1966 Cohen et a1. 96-114 NORMAN G. TORCHIN, Primary Examiner.

R. H. SMITH, Assistant Examiner. 

1. A PHOTOGRAPHIC EMULSION HAVING A LOW MODULUS OF ELASTICITY COMPRISING AN AQUEOUS DISPERSION OF SILVER HALIDE IN A BINDER COMPOSED OF APPROXIMATELY 70-97% (DRY WEIGHT) OF STYRENE-BUTADIENE LATEX AND AT LEAST 3, (DRY WEIGHT) OF HYDROPHILIC MATERIAL CONSISTING PRINCIPALLY OF GELATIN WHICH EMULSION CONTAINS 5-100, BASED ON THE TOTAL BINDER, OF COLLOIDAL SILICA THE PARTICLE SIZE OF WHICH IS LESS THAN 0.03 MICRONS. 